Spontaneous Decomposition of an Extraordinarily Twisted and Trans‐Bent Fully‐Phosphanyl‐Substituted Digermene to an Unusual GeI Cluster

Abstract Ditetrelenes R2E=ER2 (E=Si, Ge, Sn, Pb) substituted by multiple N/P/O/S‐donor groups are extremely rare due to their propensity to disaggregate into their tetrylene monomers R2E. We report the synthesis of the first fully phosphanyl‐substituted digermene {(Mes)2P}2Ge=Ge{P(Mes)2}2 (3, Mes=2,4,6‐Me3C6H2), which adopts a highly unusual structure in the solid state, that is both strongly trans‐bent and highly twisted. Variable‐temperature 31P{1H} NMR spectroscopy suggests that 3 persists in solution, but is subject to a dynamic equilibrium between two conformations, which have different geometries about the Ge=Ge bond (twisted/non‐twisted) due to a difference in the nature of their π‐stacking interactions. Compound 3 undergoes unprecedented, spontaneous decomposition in solution to give a unique GeI cluster {(Mes)2P}4Ge4⋅5 CyMe (7).


S7
Simulation of the 31 P{ 1 H} NMR spectrum of 3 at 193 K.

S9
Details of DFT calculations.

S52
Alternative views of the HOMO and LUMO of 3. Table S1. Comparison of key structural parameters (experimental and calculated) for 3. Table S2. Experimental and calculated chemical shifts (ppm) and coupling constants (Hz) for 7.
X1-Ge-Ge-X2 () from 180°, where X1 and X2 are dummy atoms which are positioned midway along the two respective P-P vectors ( Figure S1). Figure S1. Definition of the trans-bending and twist angles in 3. Figure S2. 1 H NMR spectrum of 3 in d8-toluene at 298 K.     (lower). The peak at -32.4 ppm is coincident with the peak due to the diphosphane impurity (Mes)2P-P(Mes)2 (6) and so the simulation of this peak could not be carried out accurately. Figure S8. 31 P{ 1 H} NMR spectrum of a sample of 3 in d8-toluene after 48 hours, showing substantial decomposition to 6 and 7 (labelled peaks due to 6 (*) and 5 (#)). -S9-

DFT calculations:
Geometry optimizations were performed with the Gaussian09 suite of programs (revision D.01). [S6] The B97D functional, [S7] which explicitly includes mid-to-long-range dispersive interactions, generated an optimized geometry for 3 which correlated well with the data obtained by Xray crystallography (Table S1). In view of this, ground state optimizations and frequency calculations were performed using the B97D functional with the 6-311G(2d,p) all-electron basis set [S8] on all atoms [default parameters were used throughout]. Optimization and frequency calculations on the triplet state 3T were performed at the unrestricted uB97D/6-311G(2d,p) level of theory. Automatic density fitting was employed for all geometry optimizations and frequency calculations. For the tetrylene 3C two minimum energy geometries were found, one with two pyramidal P atoms and one with one pyramidal and one planar P atom. These geometries differ in free energy by just 0.1 kJ mol -1 ; the first of these was the lower in free energy and was used for all further calculations. The global minimum energy conformation of 9 was located by a relaxed potential energy surface scan at the B97D/6-31G* level in which the P-Ge-Ge-P dihedral angle was increased in 10 increments through a 180 rotation; the located minimum energy geometry was then reoptimized at the B97D/6-311G(2d,p) level. The identity of all minima was confirmed by the absence of imaginary vibrational frequencies in each case. Natural Bond Orbital analyses were performed using the NBO 3.1 module of Gaussian09. [S9] NMR shielding tensors and coupling constants were calculated for the optimized structures of 3 and 7 (B97D/6-311G(2d,p)) using the GIAO method at the PBE1PBE/def2QZV [Ge, P], 6-31G(d,p) [C, H] level of theory; [S10] all 31 P chemical shifts were calculated relative to PMe3 at the same level of theory and are quoted relative to 85% H3PO4 (see Table S2).

NIMAG = 0
Final atomic coordinates for 3C (one planar and one pyramidal P atom):